The present invention relates to liquid crystal display devices and, more particularly, to fluorescent liquid crystal display devices comprising liquid crystal display materials and fluorescent materials dissolved therein. Light scattering conditions occur within the fluorescent liquid crystal display devices in response to external excitation such as by an electric field, whereby visible fluorescence emitted from the fluorescent material effectively escapes from the liquid crystal materials.
Generally known as electro-optical effects of liquid crystals are the dynamic scattering effect, twisted nematic electric field effect, guest-host effect, cholesteric-nematic phase transition effect, and so forth. These electro-optical effects provide displays by the scattering or absorption of ambient light, as distinguished from the effects of luminescent materials which per se produce luminescent displays such as lamp displays, luminescent diode displays, electroluminescence displays, plasma displays or the like. The displays resorting to the electro-optical effects are advantageous over those of the latter type in that they involve reduced energy consumption, but have the drawback of lacking brilliance.
The present invention has overcome the above problem and provides novel useful display devices which have the low power consumption characteristics of so-called passive displays not luminescent in themselves and which incorporate a self-luminescent component for giving a brilliant active display.
R. D. Larrabee has already proposed to add a fluorescent material to a liquid crystal material and vary the fluorescent intensity of the material by electric field (RCA Review, Vol. 34, P 329, 1973). However, his paper states that he failed to find liquid crystal materials which do not absorb ultraviolet light at room temperature. This appears attributable to the fact that when causing a fluorescent material in a liquid crystal material to absorb a varying amount of light in accordance with the orientation of the liquid crystal to vary the fluorescence intensity with the light absorption, the exciting light is absorbed by the liquid crystal layer without effectively exciting the fluorescent material.
U.S. Pat. No. 3,844,637 discloses fluorescent liquid crystal compositions comprising 4'-methoxy-(or -ethoxy-) benzylidene-4-n-butylaniline as a liquid crystal material. However, the compositions per se absorb violet light or near ultraviolet light without permitting effective excitation of the fluorescent material.